Gluon

This is the name of the particle which carries the strong force. There are 8 different kinds of gluons. Quarks change color through their interactions with the strong force (gluons) as seen here where Harold and Danny are changing colors.

Gravitational Force

One of the fundamental forces of nature. This force attracts particles that have mass. The gravitational force of attraction gets stronger for things with more mass and the closer the objects are together.